Some models of water heaters for residential and commercial use often include a large storage tank of water. To improve upon the efficiency of these boiler system designs, newer models are focused on maximizing the transfer of heat to smaller volumes of water that may be made available on demand.
To minimize the volume of water which is heated at any given time, water is heated as it passes through the continuous flow system. Because the retention time of the water within the boiler may be relatively short, it is imperative to design a system which can bring the water up to the target temperature within this short time frame. In addition with the increasing cost of fuel, there is a need to design systems which can maximize the transfer of heat from the products of combustion of fuel burners to the water flowing through the boiler and minimize the potential for heat loss.